The present invention relates to cam phasers for altering the phase relationship between valve motion and piston motion in reciprocating internal combustion engines; more particularly, to cam phasers having a vaned rotor rotatably disposed in an internally-lobed stator wherein the rotor and stator can be mechanically locked together by a locking pin; and most particularly to an apparatus and method for accurately measuring the axial position of the locking pin within its range of travel.
Cam phasers are well known in the automotive art as elements of systems for reducing combustion formation of nitrogen oxides (NOX), reducing emission of unburned hydrocarbons, improving fuel economy, and improving engine torque at various speeds. Typically, a cam phaser employs a first element driven in fixed relationship to the crankshaft and a second element adjacent to the first element and mounted to the end of the camshaft in either the engine head or block. A cam phaser is commonly disposed at the camshaft end opposite the engine flywheel. The first element is typically a cylindrical stator mounted inside a crankshaft-driven gear or pulley, the stator having a plurality of radially-disposed inwardly-extending spaced-apart lobes and an axial bore. The second element is a vaned rotor mounted to the end of the camshaft through the stator axial bore and having vanes disposed between the stator lobes to form actuation chambers therebetween such that limited relative rotational motion is possible between the stator and the rotor. Such a phaser is known in the art as a vane-type cam phaser.
The disposition of the rotor in the stator forms a first, or timing-advancing, array of chambers on first sides of the vanes and a second, or timing-retarding, array of chambers on the opposite sides of the vanes. The apparatus is provided with suitable porting so that hydraulic fluid, for example, engine oil under engine oil pump pressure, can be brought to bear controllably on opposite sides of the vanes in the advancing and retarding chambers. Control circuitry and valving, commonly a multiport spool valve, permit the programmable addition and subtraction of oil to the advance and retard chambers to cause a change in rotational phase between the stator and the rotor, in either the rotationally forward or backwards direction, and hence a change in timing between the pistons and the valves.
Under conditions of low engine oil pump pressure, such as during startup, it is desirable to mechanically lock the rotor and stator together in a default mode to prevent unwanted relative angular movement of the rotor/stator when the pump pressure is not high enough to reliably position the rotor relative to the stator. This is typically accomplished by a hydraulically activated locking pin disposed in the rotor and positioned parallel to the rotational axis of the phaser. In the default position, when the rotor and stator are locked together, a locking pin spring biases the cylindrical locking pin outward to engage a pin bore disposed in the stator. When the oil pump pressure reached a pre-determined level, the hydraulic force of the oil causes the locking pin to retract from the pin bore and into the rotor thereby decoupling the rotor from the stator and permitting cam shaft phasing to occur. When the rotor and stator are mechanically locked together in the default mode, the torsional forces applied to the stator by the engine crankshaft are transferred to the rotor/camshaft via lateral loading of the locking pin in the pin bore.
It is desirable for the pin to be retracted from the coupled mode in a predictable manner to assure that the decoupling event occurs precisely when needed. That is, when a predetermined oil pressure is reached after engine start-up. Therefore, during development and testing of the cam phaser, it is desirable to accurately measure the actual axial position of the locking pin relative to oil pump pressure in order, for example, to calibrate the locking pin spring. This measurement is difficult to obtain because the locking pin itself is buried inside the cam phaser and rotates with the cam shaft. Moreover, since space in the area of the cam phaser is limited, there is very little room to mount measuring equipment that could accurately monitor the axial position of the locking pin.
What is needed is in the art is a method of accurately measuring the axial position of the cam phaser locking pin, during xe2x80x9creal-timexe2x80x9d engine operation, to determine pin position relative to oil pump pressure exerted on the locking pin.
The present invention is directed to a vane-type camshaft phaser wherein a locking pin assembly, including a locking pin, bushing and spring, is disposed between a rotor and a stator of the phaser to selectively couple the rotor and stator together. The invention allows the axial position of the locking pin to be accurately determined through its entire range of travel by the use of a Hall-effect sensor. A permanent magnet is secured to the nose portion of the locking pin and a sensor is secured to the floor of the mating pin bore. By measuring the voltage output of the Hall-effect sensor as the magnet moves away from the sensor, the axial position of the locking pin can be determined.